This is an application for a five year project to study the life history of human aging by investigating age- specific contributions to fitness among older individuals in traditional societies. With the premise that natural selection on human aging and lifespan depends not only on direct reproduction, but also on contributions to the fitness of descendants, the proposed research will focus on the determinants and implications of intergenerational material and social transfers among the Tsimane of Bolivia. The Tsimane are Native South Americans, who practice a mix of foraging and small-scale horticulture in villages without running water and electricity. The Tsimane lifestyle shares many features with the lifeways that have been prevalent during human evolutionary history, particularly high rates of infections, natural fertility and a subsistence-based economy with low rates of caloric intake relative to energetic expenditure. The goals of the proposed research are jointly empirical, theoretical and methodological. The empirical goals are to: A) measure the material and non-material net resource flows among kin and non-kin of different generations, as they change longitudinally with age;B) link those flows to changes in short- and long term changes in physical state and to demographic outcomes, and C) assess alternative theoretical models about the determinants of lifespan among humans. The theoretical goals are to advance evolutionary economic modeling of lifespan evolution, with a specific focus on capital-based models and their relevance to humans, nonhuman primates, and the other species represented in this P01.The methodological aims of this proposal are to develop cross-culturally applicable empirical estimation procedures for converting measures of time into more valid estimates of resource transfers and changing fitness contributions withage. RELEVANCE (See instructions): The research and efforts of this Program Project will extend and expand the knowledge gained to date from the existing PO1 to humans and aging/life span. This will mutually inform aging of a variety of species.